In recent years, there is a technique for mounting an input device referred to as a touch panel or a touch sensor on a display device on a display surface side thereof and for detecting and outputting an input position of an input tool when input operation is performed in which the input tool such as a finger and a touch pen (also referred to as a stylus pen) or the like contacts the touch panel. The display device having such touch panel is widely used not only in a computer but also in a portable information terminal such as a cellular phone and the like.
As one of detection methods for detecting a contact position where the finger or the like contacts the touch panel, there is an electrostatic capacitance type detection method. An electrostatic capacitance type touch panel is configured, for example, as the following. That is, within a screen of the touch panel, there is provided a plurality of capacitance elements constituted of a pair of electrodes, which are, for example, a driving electrode and a detection electrode disposed opposite to each other interposing a dielectric layer. Then, when the input operation is performed in which the input tool such as the finger and the touch pen contacts the capacitance elements, electrostatic capacitance of the capacitance elements changes. By using this change, the input position is detected.
In a method for detecting a position of an input tool by disposing a plurality of electrodes within a screen of the touch panel and by using a change in electrostatic capacitance of a part of the plurality of electrodes caused by approaching the input tool to a part of the electrodes, an arrangement interval of the plurality of electrodes greatly affects accuracy of position detection. In particular, in a case where the input tool has a small area, output of a position detection signal tends to be small at a boundary between adjacent electrodes. In a case where the output of the position detection signal is small, it may cause a reduction of detection sensitivity or an erroneous detection of the position.
On the other hand, in a case where the arrangement interval of the plurality of electrodes is narrowed, an arrangement density of the electrodes disposed within a detection range increases. This may lead to a decreased visibility of a display image. Moreover, an increase of the number of detection circuits connected to a position detection electrode is a factor of hindering downsizing of a display device. The increase of the number of detection circuits increases a probability of failure of a part of the increased number of detection circuits.